Roof windows - size, order?

Hello,

we have bought a townhouse and soon want to install roof windows in the attic. The previous owners also gave us the original construction plans; up to four windows would have been possible, but they had only installed 2, which are also quite small (smaller than those of the neighbors).

The construction plan specifies the size as 85x140 cm.

We searched for tilt-and-turn windows at Velux, but apparently there is no window in 85 cm, only in 78 or 94 cm x 140?

What is allowed to be installed there? I want to adhere to the specifications as much as possible...

The roof is insulated up to the blue vapor barrier foil, but it is brittle from the sun. What makes the most sense to do first: renew the vapor barrier foil or install/replace roof windows?

Thanks in advance.

To my knowledge, there are no regulations for roof windows. Unless it is explicitly mentioned in the [Bebauungsplan]. But I have never read that either. So put in as much as the structural engineering allows.

Even a 78cm wide window probably won't fit without a lintel.

It's best to go to a roofer near you and look at a model to see the difference between a [Schwingfenster] and a [Klappschwingfenster].

The roofer could also evaluate your blue foil. Normally, no sun hits it.